The present invention relates to an improved subsea wellhead in which either the production string or the production tree may be easily and quickly recovered from their subsea location and readily reinstalled without the excessive loss of downtime normally associated with such operations.
Prior to the present invention, the removal of either of the production tubing or the production tree from a subsea well could only be accomplished by utilizing the steps of their installation in the reverse order for recovery. This entails substantial equipment for the removal of the tree and for the removal of the tubing string. None of the known prior art allowed the easy removal of the production tree in any manner.
One of the closest known prior art is the European Patent Specification, Application No. 92305014.0, filed by Cooper Industries, Inc. on Jun. 1, 1992, having inventors named: Thomas Gus Cassity and Hans Paul Hopper and entitled "Wellhead." This application discloses an improved wellhead in which the production tubing and tubing hanger can be retrieved without pulling the production tree. This art, however, requires that the production tubing be pulled prior to pulling the tree. There is no suggested structure or steps by which the tree can be removed, without first removing the production tubing, other than by the extended procedure which reverses its installation process.